U.S. Pat. No. 4,007,991 disclosed a system wherein two fan-shaped beams of radiation, emitted from a location at the apex of a pyramid-shaped space, were swept flatwise angularly across that space for transmitting position information to bodies present in the swept space. Each beam had its longer cross-section dimension oriented at right angles to that of the other, and each beam was swept transversely to its said long dimension. Position information encoded in modulation of each beam signified the momentary angular position of the beam in its sweep. Hence a body receiving radiation from both beams could obtain information concerning its location relative to two of the three coordinates that fully defined its position. However, for the purposes for which the system was intended there was no need for information to be available at the body concerning its distance from the radiation emitter and accordingly the patent does not disclose means for making distance information available at the body.
U.S. Pat. No. 3,484,167 disclosed a system wherein angularly sweeping beams were used for transmitting distance information as well as bearing and altitude information from a leader aircraft to follower aircraft flying formation on it. Under the operating conditions for which the system was intended, wherein follower aircraft tended to maintain well established positions relative to one another and to the leader aircraft, there was little or no likelihood that one of the follower aircraft might receive position information intended for another. The patent reflects no recognition of the problem of delivering position information exclusively to one of several bodies capable of receiving it, much less does it suggest how that problem might be solved.
An earlier system in which swept beams were used to convey information to bodies in the space swept by the beams is disclosed in British Pat. No. 1,161,027. Here again there was no attempt to restrict delivery of the transmitted information to only that one of several bodies in the swept space that was at a predetermined distance from the transmitter.
It is of course well known that when emitted radiation is reflected back to its source from a body in a space into which the radiation is emitted, the distance between the source and the body can be readily determined on the basis of the time required for the radiation to travel to and from the body. Thus, by means of so-called range gating, as pointed out in U.S. Pat. No. 3,056,129, it is possible to determine at the beam emitter station the exact position of one of several bodies in a space swept by the beams, provided the bodies are at different distances from the station and that said one body is at a predetermined distance from the station, or within a predetermined range of distances therefrom. Similarly, there is no difficulty in encoding distance information along with other position information in the modulation of a beam, as is evident, for example from the disclosures of U.S. Pat. No. 3,484,167 and U.S. Pat. No. 4,007,991.
Heretofore, however, it has not been known how to transmit such distance information exclusively to one of several bodies that might be present in the space swept by the beams, unless each body was equipped with means for accepting only information that was specifically addressed to it and it was possible to identify each individual body at the beam emitter location so that information intended only for a selected one of the bodies could be correctly addressed to it.
There are many practical applications for which a solution to this problem has been needed, some of which will be immediately apparent to those familiar with this field of art. By way of illustration, one such application--for which the present invention is especially suitable--is in connection with a system for scoring simulated firing of a fixed or mobile weapon at targets which may be fixed or moving and which are equipped with retroreflectors by which radiation emitted from the weapon location can be reflected back to that location. In that application, periodically sweeping radiation beams can be employed for ascertaining the position of a target at which the weapon has been aimed, so that the position of the target can be compared with that of an imagined projectile as it moves along a trajectory calculated on the basis of the orientation of the weapon barrel axis at the instant of simulated firing. At the instant when the imaginary projectile terminates its calculated trajectory, the same beams can be employed to transmit information to the target, from which a calculation can be made at the target of the results achieved with the simulated projectile. The calculated results can be displayed at the target, as by a simulation (e.g., smoke puff or flash) of the effects the imaginary projectile would have produced had it been a real one.
Simulated target practice equipment generally capable of performing the functions just described is disclosed in U.S. Pat. No. 3,832,791, but in the system of that patent the radiation was not emitted in the form of sweeping beams but, instead, in the form of a stationary beam that had substantial divergence. The vertical divergence of the beam was equal to the angle through which the weapon barrel could be swung in elevation, and its horizontal divergence was such that at the minimum shooting distance the beam had a width equal to the breadth of the target. The divergent beam avoided problems arising from the difference between the curving trajectory of a real projectile and the straight path of radiation, but its divergence made for low signal strength and a poor ratio of signal-to-background disturbance at the radiation detectors. With the use of sweeping fan-shaped beams that have very little divergence in one dimension transverse to the direction of propagation, high signal strength is available at all receivers, due to the low diffusion of each beam.
The divergent beam used in the prior weaponry scoring system also had the serious disadvantage that two or more radiation receivers within its relatively broad field of radiation could receive information transmitted by means of it.
This latter disadvantage was of substantial practical importance because in simulated gunnery practice exercises it is often desirable or necessary to have several targets located within a small portion of the field of view that is seen from the weapon position. By contrast, the present invention affords a satisfactory solution to the above-explained problem of selective delivery of information encoded in flatwise sweeping fan-shaped beams and thus makes it feasible to employ such beams in a system for simulated gunnery scoring, opening new possibilities for extending the scope of training with the use of such systems and increasing the accuracy and realism of scoring. With such a system, each target could comprise a reflector co-located with a detector of beam radiation. Assume, then, that several such targets were at different range distances from a weapon position from which sweeping beams were emitted but were at apparently small distances from one another in azimuth and/or elevation. With selective delivery of information to such of those targets that satisfied a range criterion for delivery of the information, beam transmissions could include information about the type of ammunition assumed to be fired, as well as information about the exact placement of the imagined projectile relative to the reflector-detector position of a target found to be at a range distance from the weapon equal to the calculated range of the imaginary projectile, and hit effects could be evaluated at the target on the basis of its own relative vulnerability. If two or more such targets happened to be at that same range distance, a similar transmission and calculation could be made for each. Such scoring--not merely of hits and misses but of precise hit effects--obviously requires delivery of transmitted information only to the detector or receiver for which it is intended, since scoring results would be confused if the transmitted information could be indiscriminately delivered to targets at any range. It is also obvious that in such a weapons practice system it would be impracticable to require information transmitted to a target to include an address specific to the particular target, since such a requirement would impose severe restrictions on target mobility and would thus limit the training value of the system.
With these considerations in mind, it is the general object of this invention to provide a method and means for transmitting information by means of modulated, fan-shaped, flatwise sweeping beams of radiation, whereby such information can be delivered exclusively to one of a plurality of bodies that are present in a space swept by the beams and are equipped for reflecting beam radiation back to the location from which the beams are emitted, a condition for such delivery being that said one body is at a distance from said location that is appropriate for its receipt of the information, and delivery of the information then being effected exclusively to that one body even though all other bodies present in that space would be capable of receiving and accepting the same information if they were at the position occupied by that one body.
A modified form of the invention is directed to the solution of the complicated special case problem that arises when two (or more) reflecting bodies present in a space being swept by such beams are simultaneously intercepted by one of the beams in a particular angular position of its sweep, and information is to be transmitted only to the one or more of said bodies that are at a distance from the transmitter location that is appropriate for its or their receipt of the information.
A further modified form of the invention is directed to the further complicated problem that arises when more than two bodies are present in the space swept by beams, and certain of those bodies--but not all of them--are at a distance from the transmitter location such that information to be transmitted is valid for said certain bodies but not for any other body.
Another important object of the invention is to provide for selective delivery of information to bodies in a space swept by flatwise angularly sweeping fan-shaped beams of radiation, with the beams serving as the transmission medium, where the particular information to be delivered to a particular body in that space is dependent upon the position of that body in range relative to a station from which the beams are emitted or upon its position relative to said station both in range and in a function of momentary angular positions of two or more of the beams at the times of their interception by the body.
The invention has other objects which will appear as the description proceeds and which are related to specific application of the use of flatwise-swept fan-shaped beams to a simulated weapons fire scoring system, to enable such a system to have substantially greater versatility than prior systems of the same general type with respect to the types of weapon fire and targets that can be simulated, and also to enable such a system to have greater accuracy in the scoring of results.
Insofar as the present invention is related to a simulated weapons fire practice system employing fan-shaped beams of radiation, it is closely related to the subject matter of my copending application Ser. No. 14,115. Insofar as the present invention is concerned with systems that may also involve the problem of unambiguous measurement of the positions of bodies that may be present in a space swept by fan-shaped beams, it is related to the subject matter of my copending application, Ser. No. 14,117. Those two copending applications thus supplement the disclosure hereof.